Teens who play contact sports, like football and soccer, are most likely to have a torn MCL. The injury happens when the outside of the knee is struck, causing it to unnaturally bend inward (toward the other knee). This creates tension on the MCL, a rope-like band, and it stretches or breaks in half.

Someone with a partially or completely torn MCL might have swelling and pain within the first 24 hours of injury. Fortunately, this injury can heal on its own with anywhere from 1 to 6 weeks of resting the joint.

Most people with an MCL injury will still need to undergo rehabilitation ("rehab") therapy to help regain strength in the joint.

What an MCL Does

The MCL is one of the four main ligaments in the knee joint. It's located on the side of the knee that is closer to the other knee. One end of the ligament is attached to the femur, while the other end is attached to the tibia.

Together with the lateral collateral ligament (LCL), which is in the same location on the outside of the knee, the MCL helps prevent the overextension of the knee joint from side-to-side.

Signs and Symptoms

Someone with a partially or completely torn MCL may or may not have symptoms, depending on the severity of the injury.

Pain and swelling can be very intense initially, and some people (with more severe injuries) will have some instability when walking, feeling "wobbly" or unable to bear weight on the affected leg.

Many people, especially those who are familiar with the injury or have torn a ligament before, report hearing a "pop" sound — the sound of the ligament tearing.

Someone who has injured a knee — whether out on the field or at home — should stop all activity (to prevent further injury) and seek immediate medical care. In the meantime, keep the area iced and elevated as much as possible to reduce swelling. Do not bear weight on the knee.

Diagnosis

At the doctor's office or emergency room, doctors will perform physical exams and imaging tests to determine if there is a knee injury and, if so, how severe it is.

To help diagnose an MCL injury, doctors do something called a Valgus test. The person lies down flat, and the doctor moves the affected leg out to the side while flexing the knee at about 30 degrees. The doctor places one hand on the back of the knee joint and the other on the top side of the ankle. The doctor then rotates the shin bone and pushes the foot outward, to see how far the MCL will extend. Too much flexibility can signal an injury.

To properly diagnose MCL injuries, doctors usually perform these tests in combination or in addition to other physical exams.

While X-rays might be taken to determine the extent of the injury, they only image bone and, therefore, can only confirm the presence of bone fractures in the knee. An MRI, which images tissue (like ligaments and muscles), can confirm a partial or complete MCL tear so some doctors will order one to confirm a diagnosis.

Types of Injuries

Doctors categorize MCL injuries according to the following criteria:

Grade I tear. This is a slight tear (or stretch) of the MCL. Both ends of the ligament are still attached to the bone, but a portion of the ligament may sag and be less taut. Recovery usually takes 1 to 2 weeks; therapy may not be needed.

Grade II tear. This is a slightly more severe tear of the MCL, with a portion of the ligament sagging. Pain and swelling is usually more severe than with a grade I tear. People usually need 3 to 4 weeks of rest and sometimes therapy.

Grade III tear. With this type of injury, the MCL breaks in half. Many people are unable to bend the knee or bear weight on it without pain. They may be unstable while walking, and the knee may sometimes "give out." People with this injury need to wear a knee brace and undergo therapy for 6 weeks or longer.

Treatment

Treating MCL injuries requires long-term resting of the joint. Depending on the severity of the injury, a person will need to walk with the assistance of crutches, limit physical activity, and wear a knee brace. Putting too much pressure on the knee can cause reinjury.

Most people do rehab at a center three times a week, with daily exercises they practice at home. For faster recovery, some people do accelerated rehab programs with more frequent therapy sessions.

In the early stages of recovery, keep the knee iced and elevated to help to reduce pain and swelling. Over-the-counter or prescription painkillers and anti-inflammatory medicine can help you deal with the pain and feel more comfortable.

While most sports are off limits — especially the activity that caused the injury in the first place — you might try some low-impact activities, like swimming, bike riding, or protected running. Talk to your doctor about what you can do. Some of these activities might even work as rehab therapy.

Coping With an MCL Injury

Being told that you can't do the things you love — like running or playing football, field hockey, or softball — can be frustrating. If you're recovering from an MCL injury, especially a severe one, you might feel angry, even depressed, especially if you can no longer play team sports with friends.

As you heal, there are ways to still feel like part of the team. Keeping score, being a coach's assistant, or bringing water to your teammates may help. Or use this as a chance to try something completely different: Start a new activity that doesn't put strain on the knee like playing the guitar, painting, or drawing.

In time, you can again do the things you love. But if you still feel frustrated or depressed about missing out on your sport, consider talking to a school psychologist or counselor.